1. Field of the Invention
The present invention relates to a color matching method when preparing a paint. More specifically, the invention relates to a method of computing the blend of plural colorants of same color and same luster as target color (or sample color) and one or plural luster color materials in a metallic and pearlescent paint (in this specification, the metallic and pearlescent paint includes both a general metallic paint, and a metallic and pearlescent paint adding a special luster color material for expressing a pearlescent effect such as mica pigment to the metallic paint), or the blend of colorants of same color as the target color in a solid color paint, by computer processing, and rationalizing the adjusting means of colors when preparing a paint.
2. Description of the Related Art
When toning a paint, the desired color must be reproduced rationally. For this purpose, in a conventional computer color matching system, the spectral reflectance of sample painted panel for primary data is measured to obtain the spectral reflectance of sample painted panel as primary data, while the calculated reflectance of color adjusted by blending plural colorants presented for coloring (adjusted color) is determined by using Kuberka-Munk optical density formula, and the absorption coefficient and scattering coefficient of visible light region are calculated from the reflectance, and the spectral reflectance when blending the colorants at a specified ratio is predicted and computed, and the calculated reflectance of adjusted color and reflectance of sample color are compared, and the blend of colorants is computed so that the adjusted color may coincide with the sample color. In this comparison, if the difference between the sample color and adjusted color is more than specified, the blend of colorants used in adjusted color is changed until the difference settles within a specified range. When the difference settles within a specified range, this blending ratio is determined as the blend value of the desired color, specifying the sample color as the target color.
In this computer color matching of paint, the sample painted panel which is the sample for obtaining primary data is a blend sample combining a chromatic colorant presented as a toning colorant to be matched with the target color, and a white pigment or luster color material to be used in combination with the toning colorant to be matched with the target color, and this sample is used as the specimen for obtaining data expressing the coloring property of the chromatic colorant to the white pigment or luster color material.
That is, for calculated computation of reflectance when blending plural chromatic colorants and white pigment or luster color material, the preliminarily measured spectral reflectance of primary data is converted into optical density K/S expressed by the ratio of absorption coefficient K and scattering coefficient S of coloring layer as film by using Kuberka-Munk formula, and the optical density in blending K/S is determined by two-constant method of Duncan""s color mixing theory, and it is further converted into the reflectance and the calculated reflectance is determined by computation.
At this time, to enhance the precision of prediction, it is converted into the reflectance in ideal state by using Sanderson""s formula for correcting effects on measurement of spectral reflectance due to inner mirror reflection or refractive index difference occurring at the interface of resin layer of film and air layer, and color mixing is computed. In order to match the blend of colorants with the target color, the adjusting method of blending ratio of colorants is realized by iterative computation by Newton-Lampson method, and further to evaluate the color coincidence of target measured reflectance and calculated reflectance, by using the color values computed from the reflectance, XYZ, L*a*b*, etc., convergence is computed by Newton-Lampson method while evaluating the difference between target value and calculated value in the metameric method, or convergence is computed while evaluating the square sum of the difference of target measured reflectance and calculated reflectance in the isomeric method.
In the prior art, blending of colorants conforming to the target color by using the computer color matching system by the above technique is computed in a specific condition, such as constant film thickness, constant base color, and constant other specific coating condition. According to the blending ratio thus obtained, an actual paint is prepared, and a painted panel is prepared according to desired conditions from the colored sample by this prepared paint, and the colored sample formed on the painted panel and the target sample are compared in color successively, and in the metallic and pearlescent paint, in addition to comparison of color, the luster of the adjusted sample is compared with the desired luster. In this comparison, when the color is not sufficiently matched, or in the metallic and pearlescent paint, if the luster is not matched sufficiently in addition to the color, the computer color matching is attempted again for correction, or colorants not matched sufficiently are blended, or in the metallic and pearlescent paint, in addition to blending of colorants, blending of luster color materials is judged visually and empirically, and is adjusted according to an empirical rule. This adjustment process is repeated until matching sufficiently with the target color and desired luster.
In the prior art, a painted panel is formed in a specific condition from the paint being adjusted in the paint manufacturing process, and by measuring its color value, computer color matching is repeated, and trials based on visual and empirical evaluation must be repeated. In such technique, in order to obtain a desired color, or color and luster, a painted panel from the paint adjusted each time must be prepared, and effects of repeatability cannot be ignored, and it takes much time and labor in preparing each painted panel, and an exclusive equipment is needed for preparing painted panels.
In the light of the problems of the prior art, it is hence an object of the invention to present a computer color matching method of paint and a preparing method of paint by using this method capable of computing the adjusted blending ratio easily and accurately, without preparing painted panels from adjusted paint, by measuring a proper blend of colorants for obtaining a desired color, or color and luster, or a proper blend of colorants and luster color materials, directly in a state of adjusted paint.